BSCI exam success, not to mention earning your CCNP, can come down to your OSPF route summarization skills. There are a few different commands and situations you need to be ready for, and one of these situations is the proper use of the “summary-address” command.\nThe summary-address command should be used on an ASBR in order to summarize routes that are being injected into the OSPF domain via redistribution. In the following example, four routes are being redisitributed into OSPF on R1, making R1 an ASBR.\ninterface Loopback16\nip address 184.108.40.206 255.0.0.0\n!\ninterface Loopback17\nip address 220.127.116.11 255.0.0.0\n!\ninterface Loopback18\nip address 18.104.22.168 255.0.0.0\n!\ninterface Loopback19\nip address 22.214.171.124 255.0.0.0\nR1(config)#router ospf 1\nR1(config-router)#redistribute connected subnets\nThese four routes are seen on downstream router R2 as External Type-2, the default for routes redistributed into OSPF.\nR2#show ip route ospf\nO E2 126.96.36.199\/8 via 188.8.131.52, 00:00:07, Serial0\nO E2 184.108.40.206\/8 via 220.127.116.11, 00:00:07, Serial0\nO E2 18.104.22.168\/8 via 22.214.171.124, 00:00:07, Serial0\nO E2 126.96.36.199\/8 via 188.8.131.52, 00:00:07, Serial0\nTo summarize networks learned by redistribution, use the OSPF command summary-address. You can probably do this summarization in your head, but do so before continuing with the lab.\nR1(config)#router ospf 1\nR1(config-router)#summary-address 184.108.40.206 252.0.0.0\nLook at the change in R2’s OSPF table.\nR2#show ip route ospf\nO E2 220.127.116.11\/6 via 18.104.22.168, 00:00:05, Serial0\nThe external routes have been successfully summarized. Note that the summary route is still marked as an E2 route.\nThere’s an interesting route installed into R1’s OSPF table as well.\nR1#show ip route ospf\nO 22.214.171.124\/6 is a summary, 00:01:51, Null0\nWhen you configure summary routes in OSPF, a route to null0 will be installed into the OSPF routing table. This helps to prevent routing loops. Any packets destined for the routes that have been summarized will have a longer match in the routing table….\nC 126.96.36.199\/8 is directly connected, Loopback17\nC 188.8.131.52\/8 is directly connected, Loopback16\nC 184.108.40.206\/8 is directly connected, Loopback19\nC 220.127.116.11\/8 is directly connected, Loopback18\nO 18.104.22.168\/6 is a summary, 00:03:10, Null0\nO 22.214.171.124\/6 is a summary, 00:07:53, Null0\n.. and packets that do not match one of the summarized routes but do match the summary route will be dropped.